The present invention relates to a method of detecting the discontinuity structures in the luminance and/or chrominance components of a video signal, with a decision criterion being derived from the environment of an image pixel so as to effect image coding with the smallest number of bits possible.
Such methods are known, for example from the book entitled "Digital Image Processing" by William K. Pratt, A Wiley Interscience Publication; John Wiley & Sons, New York, Chichester, Brisbane, Toronto, 1978, Chapter 17: "Image Feature Extraction", pages 471-499. Here various methods for detecting the discontinuities in a video signal are introduced and compared. The ability to distinguish between structures and non-structures is quite good in these various methods and the costs to implement them, for example with respect to the number of multiplications, differs. However, it is difficult with the prior art methods to detect the orientation of edges. In particular, orientations which are not horizontal, vertical or at an angle of less than 45.degree. with respect to the horizontal cannot be detected. Moreover, the prior art methods are very sensitive with respect to fixing their decision thresholds.